PHP compact Function

last modified March 13, 2025

The PHP compact function creates an array containing variables and their values. It's useful for quickly bundling variables into an array.

Basic Definition

The compact function takes variable names as arguments and creates an array where keys are variable names and values are variable values.

Syntax: compact(string|array $var_name, ...): array. It accepts one or more strings or an array of strings representing variable names.

Basic compact Example

This demonstrates creating an array from three simple variables using compact.

basic_compact.php

<?php

$name = "John";
$age = 30;
$city = "New York";

$person = compact('name', 'age', 'city');

print_r($person);

The function creates an associative array from the variables passed as arguments.

Using compact with an Array of Names

Instead of multiple arguments, you can pass an array of variable names.

compact_with_array.php

<?php

$firstName = "Alice";
$lastName = "Smith";
$email = "alice@example.com";

$vars = ['firstName', 'lastName', 'email'];
$userData = compact($vars);

print_r($userData);

This produces the same result as passing names individually. The array approach is useful when variable names are stored dynamically.

Nested Variables with compact

compact can work with nested variable names when using array syntax.

nested_compact.php

<?php

$user = [
    'name' => 'Bob',
    'profile' => [
        'age' => 25,
        'job' => 'Developer'
    ]
];

extract($user);
$result = compact('name', ['profile' => ['age', 'job']]);

print_r($result);

This shows how to compact nested variables. Note that you need to extract the array first to make variables available in the current symbol table.

compact with Undefined Variables

compact silently ignores undefined variables without throwing errors.

undefined_variables.php

<?php

$definedVar = "I exist";
$result = compact('definedVar', 'undefinedVar');

print_r($result); // Only shows definedVar

The output only contains the defined variable. This behavior can be useful when you're not sure which variables exist in the current scope.

Combining compact with extract

compact and extract can be used together for variable manipulation.

compact_extract.php

<?php

$original = [
    'title' => 'PHP Guide',
    'author' => 'Jane Doe',
    'pages' => 350
];

extract($original);
$modified = compact('title', 'author', 'pages');
$modified['edition'] = 2;

print_r($modified);

This extracts variables from an array, then compacts them back with an additional field. It demonstrates round-trip variable conversion.

Best Practices

Variable Scope: compact only works with variables in current scope.
Dynamic Names: Use array syntax for dynamic variable names.
Error Handling: Check for undefined variables if needed.
Performance: Avoid compact in tight loops with many variables.

Source

PHP compact Documentation

This tutorial covered the PHP compact function with practical examples showing its usage for creating arrays from variables.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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